The present invention relates to oil-base drilling fluids, and more particularly to invert water-in-oil emulsion drilling fluids in which the emulsifier is a reaction product of tall oil fatty acids.
In the drilling of wells by the rotary drilling technique, drilling fluid is circulated from tanks at the wellhead down the inside of the drill pipe, through the bit and back up the annulus. This patent application is directed specifically to oil-based drilling fluids, known as oil-muds, and especially those oil muds in the form of an invert emulsion.
Invert emulsions are water-in-oil emulsions in which water is dispersed in spherical form by violent agitation of an oil and water mixture in the presence of an emulsifier. In the preparation of oil muds, clay and other minerals are generally present, together with an oil such as a diesel oil or a mineral oil, and water which may range from fresh water to water containing a considerable amount of calcium chloride. Most oil muds use a calcium or magnesium fatty acid soap as the primary emulsifier. Supplemental emulsifiers, generally polyamides, are used for high temperature water and water which contains calcium chloride.
Tall oil compounds are well known as a base for invert emulsifiers. Tall oil is a by-product of the wood pulp industry, containing rosin acids and C.sub.18 acids such as oleic and linoleic acids. The most popular emulsifiers are the calcium and heavy metal soaps of rosin acids, fatty acids, fatty amines and fatty amides. The amines are quite advantageous at temperatures above 125.degree. F., as they adsorb on the clay surface to prevent breaking of the emulsions and form clay-amine complexes which resist water wetting. These complexes also develop gel strength and reduce the fluid loss of the mud.
Several methods are known for the formation of invert emulsifiers from fatty acid, such as tall oil fatty acids. Thus, according to U.S. Pat. No. 4,508,628, a polyalkylene polyamine is reacted with a mixture of fatty acids containing at least 50% by weight of C.sub.18 fatty acids, and the reaction product is then reacted with a dicarboxylic acid having from 4 to 8 carbon atoms.
According to U.S. Pat. No. 2,946,746, a polyamide emulsifying agent is prepared by reacting a polyalkylene polyamine which is at least a triethylene tetramine, with a monobasic fatty acid.
U.S. Pat. No. 3,259,572 discloses a drilling fluid containing an emulsifier which is a reaction product of a branched polyamine with an acylating agent such as a higher carboxylic acid.